Abstract
Abstract. Using Polar UVI LBHl and IMAGE FUV WIC data, we have compared the auroral signatures and polar cap open flux for isolated substorms, sawteeth oscillations, and steady magnetospheric convection (SMC) events. First, a case study of each event type is performed, comparing auroral signatures and open magnetic fluxes to one another. The latitude location of the auroral oval is similar during isolated substorms and SMC events. The auroral intensity during SMC events is similar to that observed during the expansion phase of an isolated substorm. Examination of an individual sawtooth shows that the auroral intensity is much greater than the SMC or isolated substorm events and the auroral oval is displaced equatorward making a larger polar cap. The temporal variations observed during the individual sawtooth are similar to that observed during the isolated substorm, and while the change in polar cap flux measured during the sawtooth is larger, the percent change in flux is similar to that measured during the isolated substorm. These results are confirmed by a statistical analysis of events within these three classes. The results show that the auroral oval measured during individual sawteeth contains a polar cap with, on average, 150% more magnetic flux than the oval measured during isolated substorms or during SMC events. However, both isolated substorms and sawteeth show a 30% decrease in polar cap magnetic flux during the dipolarization (expansion) phase.
Highlights
While auroral substorm signatures and open magnetic flux in the polar cap, as seen by Polar Ultraviolet Imager (UVI) and IMAGE Far Ultraviolet imager (FUV), haveFigure 1 illustrates how a keogram is created from auroral images for an isolated substorm on 4 January 2001
While the magnetometer data shows the expansion phase onset at 06:47 UT, as represented by the large red structure that starts at 06:47 UT and spans 21:00 to 03:00 magnetic local time (MLT), it does not appear in the FUV images until 06:52 UT
The isolated substorms and steady magnetospheric convection (SMC) studied here are similar in auroral intensity, extent of aurora in magnetic latitude, and amount of open magnetic flux
Summary
The keogram starts at 50 apex magnetic latitude at the bottom and goes to 90, or the magnetic north pole, at the top This configuration allows us to see the poleward and equatorward movement of the aurora at a specific MLT. When the interplanetary magnetic field (IMF) is oriented southward (Bz negative) reconnection occurs on the dayside of the magnetosphere This creates magnetic field lines that are open to the solar wind. If the merging or reconnection rates on the dayside and night side are balanced the polar cap and the amount of open magnetic flux in the magnetosphere should remain steady. (2000), a cutoff intensity of 4.3 photons/cm2/s gives a good approximation for the open-closed field line boundary when using Polar UVI LBHl data. Since we are more interested in the change in the amount of open magnetic flux this a very good representation of the changes we are looking for
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